Conventional optical semiconductor devices including an optical semiconductor element mounted therein have a configuration including a metallic lead frame 1, an optical semiconductor element 2 mounted thereon and a reflector 3 for light reflection formed of a resin material so as to surround the periphery of the optical semiconductor element 2, as shown in FIG. 1. Then, in general, a space including the optical semiconductor element 2 surrounded by the reflector 3 is encapsulated with a transparent resin such as a silicone resin. In FIG. 1, a numeral 4 denotes a bonding wire which electrically connects an electrode circuit (not shown) formed on the metallic lead frame 1 and the optical semiconductor element 2 with each other, and the bonding wire 4 is provided according to the need.
In such an optical semiconductor device, the reflector 3 for light reflection is manufactured using a thermoplastic resin represented by a polyphthalamide resin (PPA) or the like by means of injection molding. Then, a white pigment is generally blended in the foregoing thermoplastic resin to reflect the light emitted from the optical semiconductor element 2 (see Patent Document 1).
On the other hand, in the case where high heat resistance is required, a portion corresponding to the reflector 3 for light reflection is formed using mainly a ceramic material (see Patent Document 2). In this way, in the case where the portion corresponding to the reflector 3 is formed using the ceramic material, there may be the case where such formation is problematic from the viewpoints of mass production and costs of packages, and the like. In view of the foregoing matter, in forming the reflector 3, it is general to use a thermoplastic resin as described above.
In the case where a thermoplastic resin is used as a material for forming the reflector 3, the following problems arise. That is, recently, in view of the fact that a solder material to be used for mounting of an optical semiconductor device has becomes lead-free, a melting point of the solder material increases. As a result, in a surface mounting type package such as the foregoing optical semiconductor device, heat resistance to the high-temperature reflow environment is required. In consequence, with respect to a requirement of thermal deformation resistance and a requirement of thermal discoloration resistance at a solder-mounting temperature of the package, and a requirement of longer-period heat resistance due to an increase of the power of the optical semiconductor device 2, if the foregoing thermoplastic resin is used, discoloration or the like is generated at high temperatures, and following this, a lowering of light reflection efficiency, or the like becomes problematic.
In order to overcome those problems, if a thermosetting resin is used as the material for forming the reflector 3, it becomes possible to obtain a material for forming the reflector 3, which has excellent thermal discoloration resistance and which is provided with favorable light reflecting properties.    Patent Document 1: JP-A-2002-283498    Patent Document 2: JP-A-2002-232017